1. Field of the Invention
The invention relates generally to processes for creating magnetic recording medium and more particularly to processes for creating ferromagnetic metal films which have increased wear and corrosion resistance.
2. Description of the Prior Art
Magnetic recording members, such as disks, are produced by depositing thin magnetic films on a flexible or rigid substrate. The magnetic films can be composed of CoCr or NiCo. The thickness of the finished films range from ten to forty microinches. The formation of the film is commonly achieved by means of DC or RF sputtering and electron beam vacuum deposition.
U.S. Pat. No. 4,399,013, issued to Sugita et al, discloses three methods of producing a magnetic layer of CoCr by vacuum deposition. In the first method an electron gun is used to heat the CoCr to evaporation in a vacuum chamber containing a substrate. The second method adds an electric potential between the substrate and the evaporation source. A third method uses a high frequency electrode between the substrate and the evaporation source, while a positive potential is maintained at the substrate. Other examples of methods for depositing magnetic film include U.S. Pat. No. 4,260,466, issued to Shirahata et al, and U.S. Pat. No. 4,418,126, issued to Izumi et al.
The recording members formed by these processes are used for high density storage in computer systems and the reliability of the recording medium is very important. However, the thin films are subject to wear from frictional contact with the transducer head and to corrosion from deposits of foreign substances.
Attempts have been made to improve the wear characteristics of the magnetic film. For example, U.S. Pat. No. 4,345,909, issued to Takagi et al, discloses a way to produce a magnetic recording medium using chromium dioxide. Metallic chromium or chromium oxide is heated in a crucible in a highly purity oxygen atmosphere to form a cluster composed of chromium dioxide molecules. The process uses an ionized cluster beam apparatus. Another improved wear magnetic film is disclosed in U.S. Pat. No. 4,323,629, issued to Kunieda et al. The film consists substantially of Ni, Co and oxygen.
Another approach to solving the wear problem has been to form a protective overlayer on the magnetic film. U.S. Pat. No. 4,124,736, issued to Patel et al, discloses a magnetic recording member with a protective covering consisting of a barrier layer and an oxide layer. The barrier layer consists of at least one non-magnetic metal which is substantially inert under the conditions employed in forming the oxide layer. This barrier layer is primarily used to protect the magnetic film while the oxide layer is formed. The oxide layer is formed by heating a metal layer in air, oxygen, or other oxygen atmosphere at sufficient temperature and for sufficient time to form the oxide layer. This oxide layer, preferably composed of Co.sub.3 O.sub.4, has hardness and frictional characteristics which protect the magnetic film from wear.
U.S. Pat. No. 4,268,369, issued to Barlow et al, discloses a process for forming a protective layer of silicon dioxide. A substrate is covered with a magnetic film of Cobalt-Nickel, Colbalt or Colbalt-Nickel-Phosphorus. The magnetic film is then oxidized in air at temperatures from 100.degree. C.-200.degree. C. to provide an intermediate layer to facilitate good adhesion with the silicon dioxide. The silicon dioxide is then sputtered over the oxidized surface.
U.S. Pat. No. 3,498,837, issued to J. K. Alstad et al, discloses a method for forming a protective overlayer of chromium-chromium oxide. The chromium is heated in a soft vacuum of 10.sup.-3 to 10.sup.-4 mm. of Hg in an atmosphere containing oxygen. The chromium-chromium oxide layer is formed directly on the magnetic film.
U.S. Pat. No. 3,460,968, issued to G. Bate et al, discloses a method for forming a Co.sub.3 O.sub.4 overlayer on magnetic film. Magnetic film containing cobalt is placed in a temperature-humidity chamber until a cobalt oxide layer is sufficiently formed. The process must be done carefully to avoid contact of liquid water with the plated metal and prevent corrosion.
Other protective layers are disclosed in U.S. Pat. No. 4,390,562, issued to Yanagisawa; U.S. Pat. No. 4,390,601, issued to Ono et al; and U.S. Pat. No. 4,411,963, issued to Aine.
The above-mentioned protective layers reduce the wear on the magnetic film. However, none of these methods disclose a way of forming a magnetic film and a protective layer all in one sputter process.